Most of the marketed low-temperature insulating materials utilize gel obtained by adsorbing water in gelatin or water-soluble polymers such as polyvinyl alcohol or polyethylene oxide (see, Japanese Patent Laid Open Publication Nos. 56-36538 and 56-45977). Such gel solidifies too hard at low temperature and lose flexibility at low temperatures. Accordingly, this problem causes an inconvenience when such materials are used as an ice pillow substitute.
Japanese Patent Publication No. 47-18409 discloses oily gels consisting of an unvulcanized elastomeric block copolymer and paraffinic oil. Although flexible, they have a defect of inferior heat-insulating properties.
Japanese Patent Laid Open Publication No. 60-79061 discloses water-containing, water-absorbing cross-linked polymer particles dispersed in a continuous phase consisting of a teleblock copolymer elastomer and oily components, and Japanese Patent Publication No. 60-11738 discloses W/O emulsion obtained by dispersing a water dispersant in a homogeneous dispersing medium containing an oily substance with a high boiling point, natural rubber and synthetic rubber, which is gelled by cross-linking in the presence of a cross-linking agent. Although excellent in heat-insulating properties and flexible at low temperatures, they are associated with complicated processes and high cost. Further, if the amount of water is increased, the mechanical thermal stability will be lost and sometimes water will be found to separate. Moreover, they possess memory effect upon deformation, which is a problem during use.